A.

      B.

Figure 1. Stem density distributions by cycle in Gettysburg National Military Park (GETT). Cycle 1: 2007 – 2010; Cycle 2: 2011 – 2014; Cycle 3: 2015 – 2018; Cycle 4: 2019 – 2023. Figure A shows regeneration densities by size class. Figure B shows tree density by diameter at breast height (DBH) increments. Error bars are 95% bootstrapped confidence intervals to account for non-normal error. An asterisk denotes a linear DBH distribution that is indicative of long-term recruitment failure.



Figure 2. Regeneration Debt status for the most recent 4-year census (2019 – 2023) in Gettysburg National Military Park (GETT). Flat Tree Diam. Dist. stands for Flat Tree Diameter Distribution. If TRUE, the density of small trees is lower than expected due to chronic regeneration failure. Sapling/Seedling Composition is the % of total stems composed of native canopy-forming species. Sorenson is a measure of how closely the regen. layer matches canopy composition. For more details on metric calculations, thresholds and assessment of status, see Miller et al. 2023.


Figure 3. Deer browse impacts by cycle in Gettysburg National Military Park (GETT). Cycle 1: 2007 – 2010; Cycle 2: 2011 – 2014; Cycle 3: 2015 – 2018; Cycle 4: 2019 – 2023.


Figure 4. Loess smoothed changes in stem density for seedlings (A) and saplings (B) by species group and sample year in Gettysburg National Military Park. Specified loess span approximated a linear trend between consecutive sample events per panel.



Figure 5. Loess smoothed changes in tree stem density (A) and basal area (B) by species group and sample year in Gettysburg National Military Park. Specified loess span approximated a linear trend between consecutive sample events per panel.



Figure 6. Loess smoothed changes in invasive plant percent cover by guild and sample year in Gettysburg National Military Park. Specified loess span approximated a linear trend between consecutive sample events per panel.



Table 1. Average plot-level seedling and sapling stem densities (stems per m2) and stocking index (at the 2m radius scale) by cycle. Only native, canopy-forming species are included. Note that Fraxinus spp. (ash species) are no longer considered canopy-forming species. Cycle 1: 2007 – 2010; Cycle 2: 2011 – 2014; Cycle 3: 2015 – 2018; Cycle 4: 2019 – 2023. Plots are sampled in 4-year rotations, with a quarter of the plots sampled each year (i.e. a panel). The stocking index quantifies whether current regeneration densities are sufficient to restock a forest canopy. The index is a weighted sum of seedling and sapling densities where larger seedling size classes get higher weights. Cells highlighted in green are plots that meet the minimum management target of 0.25 seedlings/m2 and 0.14 saplings/m2 or have a stocking index >100. These are the same thresholds used in Figure 2 and are described in Miller et al. 2023.

table output
Seedlings per sq.m
Saplings per sq.m
Stocking Index
Plot Panel Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 1 Cycle 2 Cycle 3 Cycle 4
28 1 4.92 6.83 1.83 1.17 0.08 0.11 0.20 0.02 204.58 380.38 246.05 18.85
29 1 0.00 0.00 0.08 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.01 0.00
30 1 0.08 0.58 0.50 0.00 0.01 0.04 0.04 0.02 1.01 11.56 10.43 0.00
31 1 2.17 2.08 2.83 2.50 0.04 0.04 0.02 0.04 36.69 40.97 132.07 276.59
32 1 1.17 2.08 1.67 1.25 0.01 0.01 0.00 0.02 33.55 104.80 120.39 141.50
33 1 3.67 3.25 3.00 1.58 0.02 0.13 0.17 0.13 138.36 373.47 189.25 162.73
34 1 2.00 2.42 1.67 1.58 0.01 0.01 0.24 0.31 117.24 294.30 289.15 319.69
35 1 0.50 0.17 1.42 3.92 0.05 0.05 0.05 0.05 7.29 3.14 21.99 105.81
87 2 0.17 0.25 0.17 0.50 0.08 0.06 0.07 0.05 56.05 26.39 25.38 17.84
89 2 1.33 0.67 0.33 0.08 0.02 0.06 0.05 0.02 127.80 131.19 46.37 28.40
90 2 0.00 0.00 0.08 0.08 0.01 0.02 0.04 0.00 7.41 14.83 8.42 1.01
91 2 1.25 1.33 1.00 0.83 0.15 0.24 0.24 0.00 98.77 233.73 177.94 15.71
92 2 0.67 0.75 1.08 0.42 0.06 0.05 0.04 0.04 10.43 13.57 19.85 25.13
93 2 0.50 0.25 0.42 0.25 0.13 0.12 0.11 0.08 51.52 39.96 34.68 5.28
96 2 2.08 2.75 1.83 1.42 0.02 0.08 0.13 0.22 159.22 456.91 365.18 232.48
97 2 0.42 0.17 0.08 0.83 0.02 0.00 0.05 0.07 14.70 54.41 31.67 104.05
167 3 0.67 0.42 0.25 0.00 0.04 0.02 0.02 0.01 11.56 8.42 5.28 0.00
168 3 0.00 0.00 0.08 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.01 0.00
169 3 0.08 0.08 0.00 0.00 0.01 0.01 0.01 0.01 1.01 1.01 0.00 0.00
170 3 0.17 0.42 0.42 0.42 0.00 0.01 0.02 0.04 2.14 15.83 14.70 25.26
171 3 1.17 0.17 0.08 0.00 0.00 0.00 0.00 0.00 19.85 2.14 1.01 0.00
173 3 0.67 1.17 0.83 0.50 0.02 0.08 0.05 0.06 78.67 106.19 60.82 22.12
174 3 0.42 0.42 0.50 0.00 0.00 0.00 0.00 0.00 6.28 8.42 29.28 0.00
175 3 2.83 2.17 2.08 0.92 0.00 0.00 0.00 0.00 51.27 37.70 32.42 15.71
252 4 0.00 0.00 0.08 0.17 0.00 0.00 0.00 0.00 0.00 0.00 1.01 2.14
253 4 0.58 0.67 0.50 1.00 0.18 0.17 0.05 0.14 214.51 174.42 37.82 81.30
254 4 0.33 0.08 0.25 0.33 0.00 0.01 0.01 0.01 4.15 8.42 10.56 5.28
255 4 0.92 1.00 1.50 1.42 0.01 0.05 0.08 0.11 38.70 68.36 176.31 121.77
256 4 0.17 0.08 0.33 0.25 0.00 0.00 0.00 0.00 2.14 1.01 5.28 4.15
257 4 0.25 0.25 0.17 0.00 0.08 0.11 0.08 0.07 27.52 33.80 31.67 14.83


Table 1 (cont.). Average plot-level seedling and sapling stem densities (stems per m2) and stocking index (at the 2m radius scale) by cycle. Only native, canopy-forming species are included. Note that Fraxinus spp. (ash species) are no longer considered canopy-forming species. Cycle 1: 2007 – 2010; Cycle 2: 2011 – 2014; Cycle 3: 2015 – 2018; Cycle 4: 2019 – 2023. Plots are sampled in 4-year rotations, with a quarter of the plots sampled each year (i.e. a panel). The stocking index quantifies whether current regeneration densities are sufficient to restock a forest canopy. The index is a weighted sum of seedling and sapling densities where larger seedling size classes get higher weights. Cells highlighted in green are plots that meet the minimum management target of 0.25 seedlings/m2 and 0.14 saplings/m2 or have a stocking index >100. These are the same thresholds used in Figure 2 and are described in Miller et al. 2023.

table output
Seedlings per sq.m
Saplings per sq.m
Stocking Index
Plot Panel Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 1 Cycle 2 Cycle 3 Cycle 4
258 4 0.42 0.17 0.08 0.42 0.00 0.04 0.02 0.04 8.42 25.38 15.83 21.11
259 4 0.00 0.42 0.42 0.67 0.05 0.06 0.05 0.02 0.00 6.28 9.42 15.71
356 2 - 2.75 2.92 2.75 - 0.38 0.44 0.38 - 423.36 488.71 310.89


Table 2. Average % cover and number of invasive species detected in each plot by cycle. Cycle 1: 2007 – 2010; Cycle 2: 2011 – 2014; Cycle 3: 2015 – 2018; Cycle 4: 2019 – 2023. Plots are sampled in 4-year rotations, with a quarter of the plots sampled each year (i.e. a panel). Plots with at least 10% average cover or 4 or more invasive species present are in yellow. Average cover and species counts may be increasing over time due to protocol changes, including additions to the indicator species list over time, a plot search for indicator species starting in 2009 and all woody species being sampled in quadrats starting in 2019. More details can be found in the MIDN Summary of Major Protocol Changes

table output
Average % Cover
Number of Species per Plot
PlotCode PanelCode Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 1 Cycle 2 Cycle 3 Cycle 4
28 1 8.03 6.52 19.18 32.45 3 4 6 10
29 1 3.69 1.99 30.17 76.27 3 5 6 10
30 1 67.89 34.15 54.94 54.01 5 6 8 8
31 1 7.21 6.75 22.68 11.53 1 2 7 8
32 1 0.29 21.58 28.00 38.15 1 5 8 9
33 1 5.67 11.47 9.13 4.20 2 5 6 8
34 1 19.48 3.68 6.30 3.18 4 5 6 9
35 1 17.21 23.36 29.52 30.01 3 5 5 8
87 2 4.49 15.25 4.38 17.60 3 7 8 8
89 2 18.72 15.43 13.46 20.26 5 7 8 12
90 2 27.57 31.19 36.16 76.49 6 8 8 8
91 2 2.17 2.57 6.97 20.44 4 6 9 8
92 2 2.05 13.68 20.23 18.09 2 6 8 9
93 2 8.75 11.79 31.42 47.96 4 4 8 9
96 2 14.62 3.03 3.27 4.07 5 7 6 9
97 2 53.07 41.46 68.58 70.36 5 6 7 11
167 3 4.55 3.24 3.73 1.51 10 10 9 7
168 3 61.27 70.37 75.51 69.68 6 6 6 7
169 3 3.19 7.71 5.10 14.02 5 6 7 9
170 3 25.20 24.57 26.16 45.57 7 5 7 8
171 3 26.45 24.12 25.24 24.73 7 5 7 8
173 3 35.27 30.73 15.78 8.39 10 10 12 12
174 3 36.17 72.79 67.49 48.10 7 8 6 8
175 3 3.89 0.40 1.09 3.23 5 5 5 8
252 4 8.48 35.08 18.65 50.95 4 6 5 8
253 4 1.02 12.22 0.42 10.89 3 7 6 8
254 4 2.10 3.52 6.91 2.69 3 7 7 9
255 4 23.81 42.46 17.42 6.79 4 5 7 8
256 4 15.46 46.50 44.23 64.18 5 6 5 9
257 4 0.98 16.29 9.33 3.78 4 8 9 7



Table 2 (cont.). Average % cover and number of invasive species detected in each plot by cycle. Cycle 1: 2007 – 2010; Cycle 2: 2011 – 2014; Cycle 3: 2015 – 2018; Cycle 4: 2019 – 2023. Plots are sampled in 4-year rotations, with a quarter of the plots sampled each year (i.e. a panel). Plots with at least 10% average cover or 4 or more invasive species present are in yellow. Average cover and species counts may be increasing over time due to protocol changes, including additions to the indicator species list over time, a plot search for indicator species starting in 2009 and all woody species being sampled in quadrats starting in 2019. More details can be found in the MIDN Summary of Major Protocol Changes

table output
Average % Cover
Number of Species per Plot
PlotCode PanelCode Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 1 Cycle 2 Cycle 3 Cycle 4
258 4 1.02 8.79 1.09 42.54 4 5 6 11
259 4 0.77 5.35 7.12 3.58 4 3 3 6
356 2 - 0.00 0.16 1.63 - 3 3 5





Table 3. Number of plots out of 33 where priority invasive species were detected. Cycle 1: 2007 – 2010; Cycle 2: 2011 – 2014; Cycle 3: 2015 – 2018; Cycle 4: 2019 – 2023. Species on the list include all exotic vascular plant species that are capable of dominating Eastern US forest habitats, and does not include all exotic species detected in MIDN forest plots. Average cover and species counts may be increasing over time due to additions to the protocols, including a plot search for additional indicator species starting in 2009 and all woody species being sampled in quadrats starting in 2019. Species have also been added to the indicator list over time. More details can be found in the MIDN Summary of Major Protocol Changes

table output
Latin Name Common Name Cycle 1 Cycle 2 Cycle 3 Cycle 4
Acer platanoides Norway maple 3 2 3 8
Ailanthus altissima Tree of heaven 3 2 4 10
Alliaria petiolata garlic mustard 15 15 20 25
Berberis thunbergii Japanese barberry 17 24 26 28
Berberis vulgaris common barberry 0 1 0 0
Celastrus orbiculatus oriental bittersweet 1 2 5 17
Euonymus burningbush 0 1 1 14
Euonymus fortunei climbing euonymus 0 1 0 1
Ligustrum privet 3 17 15 18
Lonicera - Exotic honeysuckle - exotic 6 10 17 15
Lonicera japonica Japanese honeysuckle 29 31 31 32
Microstegium vimineum Japanese stiltgrass 25 26 32 31
Oplismenus hirtellus ssp. undulatifolius wavyleaf basketgrass 0 0 0 2
Persicaria longiseta Oriental lady's thumb 7 12 21 18
Persicaria perfoliata Asiatic tearthumb 0 1 2 7
Rosa multiflora multiflora rose 26 32 31 33
Rubus phoenicolasius wine raspberry 9 16 14 19



Table 4. Invasive plant and pest/pathogen early detections in Gettysburg National Military Park observed in the most recent census of each plot. Coordinates are in UTM NAD83 Zone 18N.

table output
Plot Year X Y Latin Name Common Name Type
GETT-256 2023 307348 4405807 Oplismenus hirtellus ssp. undulatifolius wavyleaf basketgrass graminoid
GETT-097 2022 307117 4411757 Oplismenus hirtellus ssp. undulatifolius wavyleaf basketgrass graminoid
GETT-175 2022 308602 4406809 Ailanthus altissima Tree of heaven tree
GETT-253 2023 308096 4406818 Ailanthus altissima Tree of heaven tree
GETT-169 2022 308610 4407043 Ailanthus altissima Tree of heaven tree
GETT-171 2022 309851 4408809 Ailanthus altissima Tree of heaven tree
GETT-031 2019 306841 4407290 Ailanthus altissima Tree of heaven tree
GETT-089 2022 310343 4410057 Ailanthus altissima Tree of heaven tree
GETT-032 2019 307589 4406049 Ailanthus altissima Tree of heaven tree
GETT-091 2022 308602 4407302 Ailanthus altissima Tree of heaven tree
GETT-258 2023 310104 4409815 Ailanthus altissima Tree of heaven tree
GETT-096 2022 307607 4407317 Ailanthus altissima Tree of heaven tree
GETT-033 2019 310357 4409298 Albizia julibrissin silktree tree
GETT-028 2019 310101 4409555 Albizia julibrissin silktree tree
GETT-257 2023 306605 4412050 Albizia julibrissin silktree tree
GETT-255 2023 308845 4408550 Albizia julibrissin silktree tree
GETT-033 2019 310357 4409298 Agrilus planipennis emerald ash borer pest
GETT-093 2022 307603 4413545 Agrilus planipennis emerald ash borer pest
GETT-087 2022 309127 4408804 Agrilus planipennis emerald ash borer pest